The invention relates to hydrophilic aliphatic polyurethane foams which are obtainable by reaction of specific low-monomer prepolymers and hydrophilic polyisocyanates in the presence of water. Owing to their absorptive properties, the polyurethane foams are particularly useful in the manufacture of wound dressings, cosmetic articles or incontinence products.
EP-A 949285 describes the reaction of polyisocyanates with primary diamines, low molecular weight polyols and high molecular weight polyols. This reaction does not preclude the possibility that appreciable portions of the isocyanate-reactive substances are not converted and are subsequently extractable from the hydrophilic foam.
GB 1571730 describes the reaction of high vapour pressure diisocyanates such as isophorone diisocyanate (IPDI) and bis(isocyanatocyclohexyl)methane (HMDI) with polyols. Again, unconverted components are left behind. Moreover, using free, non-derivatized diisocyanates is problematic from an occupational hygiene viewpoint. WO 2004013215 likewise utilizes volatile diisocyanates.
WO 2003/097727, U.S. Pat. Nos. 5,065,752 and 5,064,653 describe the foam-forming reaction of prepolymers in the presence of acrylamide-acrylic acid copolymers. These products are not chemically attached and are completely extractable, which is not desirable.
In U.S. Pat. Nos. 3,903,232 and 3,88,941, prepolymers are reacted with polyethers. Again, there is a risk of unattached polyols being produced. U.S. Pat. No. 5,296,518 similarly describes the reaction of prepolymers with polyethers wherein three different polyols are used, which calls the economics of this process into question. Furthermore, the process described therein is incapable of making certain that there are no low molecular weight isocyanates left in the mixture, which would not be desirable. The preparation of the prepolymers usually requires uneconomically long reaction times.
The as yet unpublished European patent application of application number 08012372.2 describes hydrophilic aliphatic polyurethane foams based on low-monomer prepolymers. However, the hydrophilicity of the resulting foams is limited. EP 08012372.2 does not disclose any polyurethane foams containing additional hydrophilic polyisocyanates.
Either the known polyurethane foams have an inadequate imbibition ability in respect of hydrophilic fluids, or they contain extractable substances that have to be classified as problematical with regard to their cell compatibility.